There are a few (IMO) major points I would like to reiterate and suggest for everyone's consideration.
Regarding the Universal "Matter" or "Patient": After learning various methods for obtaining the alchemical Agent (Spiritus Mundi, Astral Spirit, Celestial Niter, etc), I increasingly realized the significance (in terms of Quality) of the Patient Matter that must
also enter the Alchemical Equation. While various matters can be worked with (indeed, the Seeds of Nature are present in
all unprocessed matter), there is a "Primordial" Matter ("Virgin Earth" or "Adamic Earth", etc.) which can be separated from all the other matters in which it is "hidden". Some methods of separating this "Universal Matter" are more violent and destructive, others are gentle and relatively easy.
Many practitioners work with various legit matters containing this Universal Matter, but there will be more "feces" to be discarded in the process. And the good alchemical texts all tell us that this matter is everywhere, and they are all correct. This Universal Matter, awakened, reincrudated and nourished by the Alchemical Agent, then becomes our "Saturn" or our "Antimony" or our "Prima Materia" (symbolized by a cross within a circle, i.e. "Niter/Agent" & "Salt/Patient"), it becomes our "Magnet" or our "Magnesia", which will henceforth serve as the Material Alchemical "Vessel" to eventually be evolved into a full-fledged Philosopher's Stone.
Regarding the Universal Agent or "Astral Spirit" or "Celestial Niter": For
anything to be manifest/corporified/incorporated, we
always require the Sulfur Principle. It is what allows for tangible fixation and formation of
all matter, and for the expression of the ONE THING in diversity and multiplicity. When corporifying the Universal Spirit, the "rules" are the same as they are for
all matter. A Sulfur Principle is required. We
must abide by this inevitable "trade-off". The is NO such thing as "pure SM". There will always be a "signature" of the fixing Sulfur Principle. And the more subtle our fixing Sulfur Principle is, the less pronounced the signature and the less "specified" our Agent will be.
For example, a predominantly Lunar Sulfur is better, because it is more subtle and volatile than a Solar one. That's why it is sometimes said that our Spiritus, while gender-less in its incorporeal state, is more "female" (i.e. lunar) upon its first/initial corporification. It only later acquires the Solar Component, e.g. "Diana" and "Apollo". This is also the reason I tend to somewhat differentiate between a super-subtle Celestial Niter/Astral Spirit and a "Mineral Mercury". While they are
all basically carriers/containers/incorporating vehicles for Spiritus Mundi, a "Mineral Mercury" will carry more "signature" and specification from the Mineral Sulfur(s).
Many Alchemists are extracting such Mineral Mercuries from so-called "White Metals" or "White Minerals", because of their more subtle and volatile Lunar Sulfurs, and then proceed to "extract" the more Solar Sulfur from the more Red/Solar Metals, gold being a favorite for many because of its high quality Sulfur. One such Path example
HERE. But the extracted products will nevertheless still carry the mineral/metallic signatures and specifications. It's just the way those Principles work in Nature, regardless of our opinions and wishful thinking.
Using these guidelines, it is easier to decipher what various alchemical authors are talking about.
If they tell us to seek the Agent in the Mineral/Metallic Kingdom, the are most likely talking about Chemical/Chymical mineral (or metallic) extractions, often using highly ingressive/aggressive (even toxic/violent) chemicals, and subsequently re-distilling the Mineral Mercury off the chymical solvent, sometimes requiring further "purifications" via repeated distillations/rectifications, sometimes with a "binding agent" in the boiling flask that binds the solvent to itself (or neutralizes it) and only allows for the Mercurial Spirit to rise and re-condense in the receiver.
But if the authors tell us to seek the Agent in the "Sea of the Wise", it's more likely they are guiding us towards the Aether itself, for which sulfur-poor (much less specified) mediums in the gaseous state are excellent intermediaries.
A good thing to keep in mind is that while
method-specific texts (or forum posts) may vary quite a bit, the good
principle-specific texts are always the same. Recipes and processes arise from principles, not the other way around.